Display systems manipulate light to form images of text, graphics and other visual scenes. Light propagation involves a complex variety of phenomena including wave properties and polarization. In related applications, U.S. Ser. Nos. 10/904,766, 11/161,452 and 11/336,277, a new class of display engines called “polarization light modulators” was introduced. Polarization light modulators comprise polarization interferometers combined with MEMS (micro-electromechanical systems) devices that shift the phase of optical waves.
A polarization light modulator display relies on interferometry to modulate pixels in a displayed image. Interferometry in turn depends on manipulating the phase of light to produce constructive or destructive interference.
In these new systems a linear array of MEMS optical phase shifting devices serves to modulate a line of pixels in a displayed image. A polarizing beam splitter acts as both the polarizer and the analyzer in an interferometer while a polarization displacement device divides polarized light from the polarizer into orthogonal polarization components. The MEMS optical phase shifting device array imparts a relative phase shift onto the polarization components and returns them to the polarization displacement device where they are recombined and sent to the analyzer. The MEMS optical phase shifting devices are electronically controlled and convert electronic image data (light modulation instructions) into actual light modulation.
In light modulators disclosed in U.S. Ser. Nos. 10/904,766 and 11/161,452, the direction of polarization displacement is parallel to ribbons or cantilevers in the MEMS optical phase shift device. This means that light forming a particular pixel comes from light that was reflected from different parts of a single ribbon or cantilever.
In light modulators disclosed in U.S. Ser. No. 11/336,277 orthogonal polarizations are displaced perpendicular to ribbons or cantilevers in a MEMS optical phase shift device. Accordingly, light forming a displayed pixel comes from light reflected from more than one ribbon or cantilever.
Independent of polarization and interferometric control, brightness and contrast are characteristics of displays that are in need of continual improvement. Part of the art of achieving high display brightness involves matching the optical characteristics of light sources and light modulators. As light sources with improved performance become available, light modulators and optical systems must be developed to take advantage of the improvements.
Displays require innovative optical schemes for illumination and imaging of ribbon-based MEMS light modulators to achieve maximum performance.